(1) Field of the Invention
The invention relates to a method of defining a dielectric layer thickness over DRAM peripheral circuits and etching contact openings therethrough which have a desired aspect ratio.
(2) Description of the Prior Art
It is recognized in the integrated circuit technology the importance of the aspect ratio of electrical contacts. The aspect ratio is defined as the ratio of the depth of the opening to the width of the opening. The problem is becoming increasingly more difficult as the feature size, that is the width term is getting smaller while the depth term is becoming greater. The result of high aspect ratio openings is the need for better metallurgy processes to properly fill these contact openings to make the needed electrical contact to the regions at the bottom of the opening. An example of this advance of metallurgy processing is shown in U.S. Pat. No. 4,970,176 by Tracy et al.
There has been great progress in the development of DRAM integrated circuits over the recent years. The stacked capacitor has been particularly improved so as to maintain the desired capacitance while still reducing the dimensions of the cell array. Examples of improvements in stacked capacitors can be understood by reference to U.S. Pat. No. 5,110,752 by C. Y. Lu and to U.S. Pat. No. 5,126,916 to H. H. Tseng.
However, with this important DRAM progress in the cell array portion of the integrated circuit there have resulted problems, particularly in the peripheral circuits wherein very high contact aspect ratios are present. The obvious way to overcome these problems is to improve the metallurgy processes as described above. This approach does require new and more difficult to control processes to be brought into manufacturing.
It is an object of this invention to provide methods to overcome the DRAM peripheral circuit contact aspect ratio problem without using complex metallurgy processes.
It is a further object of this invention to provide a method which improves the contact aspect ratio in the peripheral circuits by reducing the height of the contact opening in a new way.